GM Service Manual Online
For 1990-2009 cars only

Circuit Description

The body control module (BCM) applies a ground through the brake sensor reference low circuit to the brake pedal position (BPP) sensor. The BCM supplies a 5-volt reference through the brake sensor reference voltage circuit to the brake position sensor. When the brake pedal is being applied, the BPP sensor then sends a variable voltage signal through the brake sensor signal circuit to the BCM.

DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC C0870 Device Voltage Reference Output Circuit

Conditions for Running the DTC

The battery voltage must be between 9-16 volts.

Conditions for Setting the DTC

C0870 03

A short to ground or an open in the BPP sensor voltage reference circuit is present.

C0870 07

A short battery positive voltage in the BPP sensor voltage reference circuit is present.

Action Taken When the DTC Sets

The stop lamps will not function correctly.

Conditions for Clearing the DTC

    • The DTC will clear on current status after the condition for setting the fault is corrected.
    • A history DTC will clear after 100 consecutive ignition cycles without a fault present.
    • A history or current DTC can be cleared using a scan tool.

Diagnostic Aids

Perform a visual inspection for loose or poor connections at all related components. Refer to Testing for Intermittent Conditions and Poor Connections .

Step

Action

Yes

No

Schematic Reference: Exterior Lights Schematics

Connector End View Reference: Master Electrical Component List

1

Did you perform the Diagnostic System Check - Vehicle?

Go to Step 2

Go to Diagnostic System Check - Vehicle

2

  1. Install a scan tool.
  2. Turn ON the ignition, with the engine OFF.
  3. With a scan tool, observe the brake position sensor parameter in the data list for the body control module (BCM).
  4. Apply and release the brake pedal.

Does the scan tool display a change in the voltage?

Go to Testing for Intermittent Conditions and Poor Connections

Go to Step 3

3

Is DTC C0870 03 present?

Go to Step 6

Go to Step 4

4

  1. Turn OFF the ignition.
  2. Disconnect the BCM harness connector C2.
  3. At the BCM harness connector C2, connect a test lamp between the brake sensor voltage reference circuit and ground.

Does the test light illuminate?

Go to Step 5

Go to Step 10

5

Test for a short to battery positive voltage in the brake sensor voltage reference circuit. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

Go to Step 12

Go to Step 7

6

Test for a short to ground or an open on the brake sensor reference voltage circuit. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

Go to Step 12

Go to Step 7

7

Inspect for a high resistance or a poor connection at the harness connector of the brake position sensor. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs .

Did you find and correct the condition?

Go to Step 12

Go to Step 8

8

Important: After replacing the brake pedal sensor, perform the calibration procedure. Refer to Brake Pedal Position Sensor Calibration .

Replace the brake pedal position (BPP) sensor. Refer to Brake Pedal Position Sensor Replacement .

Did you complete the replacement?

Go to Step 9

--

9

  1. Install a scan tool.
  2. Turn ON the ignition, with the engine OFF.
  3. Apply and release the brake pedal.

Does DTC C0870 reset?

Go to Step 10

Go to Step 12

10

Inspect for a high resistance or a poor connection at the harness connector of the BCM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs .

Did you find and correct the condition?

Go to Step 12

Go to Step 11

11

Replace the BCM. Refer to Control Module References for replacement, setup, and programming.

Did you complete the replacement?

Go to Step 12

--

12

  1. Use the scan tool in order to clear the DTCs.
  2. Operate the vehicle within the Conditions for Running the DTC.

Does the DTC reset?

Go to Step 2

System OK